Combos are certain actions that lead into each other and enhance each other, the second action in a chain will have a dotted yellow linek around it once the initiating action is activated and you have a set time to hit the second one.
You can adjust your User Interface using the HUD page which is accessed thru the System icon lower right on your set of icons at the very bottom right of the default UI set up. Or thru Options. If you click on one of the UI Boxes or elements in the HUD screen with the Cntrl + Home keys hit, you will be able to make that box larger or smaller and you can move it around and save the new location. Experiment and you will see ...or check for a thread here called Adjusting UI ...which i set up last night and has some good info on this, probably four or five pages back by now. Maybe moreEnjoy. And Welcome!